CBSE 2025 · Region 1 · Set 3 · Q26 · 3 marks
(a)Mention any three features of results of experiment on photoelectric effect which cannot be explained using the wave theory of light.(b)In his experiment on photoelectric effect, Robert A. Millikan found the slope of the cut-off voltage versus frequency of incident light plot to be $\displaystyle 4.12 \times 10^{-15}$ Vs. Calculate the value of Planck's constant from it.
(a)
Mention any three features of results of experiment on photoelectric effect which cannot be explained using the wave theory of light.
(b)
In his experiment on photoelectric effect, Robert A. Millikan found the slope of the cut-off voltage versus frequency of incident light plot to be $\displaystyle 4.12 \times 10^{-15}$ Vs. Calculate the value of Planck's constant from it.
Marking-scheme solution
(a)
Three features:
(i)
The existence of threshold frequency $\displaystyle \left(\nu_{0}\right)$.
(ii)
Maximum kinetic energy of photoelectrons is independent of intensity of incident radiation.
(iii)
Instantaneous nature of photoelectric effect.
(b)
slope $\displaystyle =\frac{h}{e}$
$\displaystyle \therefore h=e \times$ slope
$\displaystyle =1.6 \times 10^{-19} \times 4.12 \times 10^{-15}$
$\displaystyle =6.6 \times 10^{-34} \mathrm{~Js}$
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CBSE Class 12 Physics past-paper question from the 2025board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.